Heart failure affects millions of people worldwide. Heart failure often manifests itself in relatively wide QRS signals, signifying a desynchronization between electrical activation of the right and left ventricles. Often, a left bundle branch block (LBBB) interrupts the normal conduction path to the left ventricle and results in the intrinsic conduction taking a relatively long time to reach the left ventricle, causing it to be activated well after the right ventricle. This dissynchrony results in a very inefficient contraction, resulting in very low cardiac output and patients who are unable to be very active. Over time, heart failure will progressively worsen and lead to death.
While some drug therapies may help some patients, electrical stimulation is more beneficial for those patients, assuming they meet certain criteria. Such stimulation is referred to as cardiac resynchronization therapy (CRT), which typically involves delivering electrical stimulation to the left ventricle prior to intrinsic conduction reaching the left ventricle, which results in a more synchronized contraction of the ventricles. CRT may include bi-ventricular therapy where electrical energy is delivered to both the right and the left ventricle. While delivery of energy to the right and left ventricles may occur simultaneously, in general, a delay exists, which is often referred to as an interventricular delay or interventricular pacing delay (VV delay).
For patients who meet the current CRT implant criteria, a relatively large percentage (about 30%) of those patients do not respond to CRT. Various reasons exist for a patient's failure to respond to CRT. For example, a patient's failure to respond may be due to cardiac condition or due to factors dictated by implementation of CRT. In particular, a lack of adequate capture assessment for bi-ventricular pacing is one reason a patient may fail to respond to CRT. Fusion between an intrinsic wavefront and an evoked response or between evoked responses can complicate capture assessment. If fusion is caused by VV timing, changing the VV delay may delivery non-optimal CRT and may even post some clinical risks. Further, if an RV pacing site and an LV pacing site are too close to each other, detection of an evoked response or evoked responses may be difficult. Consequently, a capture detection algorithm may fail to distinguish capture from non-capture or inadvertently label capture as loss of capture. In turn, such a failure may cause an implantable device to perform unnecessary actions or to adjust one or more therapy parameters in a non-optimal manner.
As discussed herein, various exemplary techniques aim to improve delivery of CRT by enabling or disabling a capture detection algorithm and/or by determining one or more CRT parameters that allow for adequate capture assessment. Other exemplary techniques are also discussed.